Patent Application
20130016703
The exemplary and non-limiting embodiments of this invention relate generally to wireless communication systems, methods, devices and computer programs, and more specifically relate to allocating a same identifier to multiple user equipments in a cell.
The following abbreviations used in the specification and/or the drawings are defined as follows:
In the E-UTRAN system as well as many other radio access technologies, users are assigned a temporary identifier for use while in a cell. As smartphones and other portable interne appliances which enable mobile email, navigation and browsing have become more commonplace, many cells manage a radio environment in which there are a high number of concurrent users transferring relatively small amounts of data. Adding to this number of low volume users are smartphones which have applications such as social networking services running in the background that routinely set up a wireless connection to exchange data even without active user input.
In the LTE system such devices are in the RRC-CONNECTED state with the network access node in the cell, which assigns or otherwise allocates a C-RNTI to each mobile device as its temporary identifier. Since these C-RNTIs are used to distinguish one device in the cell from all others, each C-RNTI uniquely identifies the devices operating in the cell. Much research has gone into increasing the sheer data capacity of such radio systems but in the above scenario a limit of unique C-RNTIs available in the cell is often reached before any limit on data throughput. It is altogether possible that a newly entering device can potentially be denied connection in a cell for lack of any C-RNTIs available to allocate to it.
Embodiments of these teachings mitigate the above problem.
In a first exemplary embodiment of the invention there is an apparatus comprising a processing system comprising at least one processor, and a memory storing a set of computer instructions. In this exemplary embodiment the processing system is arranged to: assign to a first user equipment and to a second user equipment a same temporary identifier for use at least while the first and the second user equipments are simultaneously in a connected state in a same cell; and selectively associate individual control channel transmissions utilizing the temporary identifier to only one of the first and the second user equipments according to a predetermined time domain division.
In a second exemplary embodiment of the invention there is a method comprising: assigning to a first user equipment and to a second user equipment a same temporary identifier for use at least while the first and the second user equipments are simultaneously in a connected state in a same cell; and selectively associating individual control channel transmissions utilizing the temporary identifier to only one of the first and the second user equipments according to a predetermined time domain division.
In a third exemplary embodiment of the invention there is a computer readable memory storing a computer program, in which the computer program comprises: code for assigning to a first user equipment and to a second user equipment a same temporary identifier for use at least while the first and the second user equipments are simultaneously in a connected state in a same cell; and code for selectively associating individual control channel transmissions utilizing the temporary identifier to only one of the first and the second user equipments according to a predetermined time domain division.
These and other embodiments and aspects are detailed below with particularity.
While the exemplary embodiments of the invention detailed below are in the context of the C-RNTI which is used in the LTE system, these are simply examples and not limiting to the broader teachings herein. Various other systems use differently named temporary identifiers to distinguish mobile user devices operating in the cell and these teachings can be used to extend the number of users that a fixed number of such temporary identifiers can service. Such other systems are not limited to only cellular-type systems but also apply for wireless local area networks and other non-cellular radio access technologies.
One possible way to solve the C-RNTI limitation detailed above in the background section is to increase the number of C-RNTIs available in a cell. A similar approach was done in the past to increase the possible number of globally unique identifiers associated with the network access nodes themselves. In the past hexadecimal digits replaced previous base-10 digits to increase the number but also the number of bits allocated for a given identifier can also be used to allow for expanding the number of identifiers. This is seen as a bit difficult to implement since legacy equipment is often unable to be adapted by a simple software download to the newer system and also the old and new numbering system must be able to exist side by side for some transition period.
These teachings take a different approach to resolve or at least mitigate the problem, namely by re-using the same temporary identifier value for two or more user devices (more generally UEs) in the cell and distinguish them from one another in the time domain, such as by radio frame or subframe numbers.
As a brief overview, assume a first and a second UE are each allocated the same C-RNTI #x. Both of those UEs are in a RRC-CONNECTED state with the same cell at the same time. When the network sends control signaling such as a radio resource allocation schedule PDCCH to the first UE it will send it in a radio frame or subframe associated with the first UE. The first UE will interpret the C-RNTI #x sent on the PDCCH as its own identity only if that PDCCH is sent in a radio frame/subframe associated with the first UE. The second UE will not be looking for a PDCCH addressed to it during those times since the time division of these two UEs is mutually exclusive on the control channel
The network can enforce this time division quite easily, such as for example when assigning discontinuous reception DRX periods to these UEs. Other examples for implementing this time domain separation are detailed further below, such as the system frame number and subframe number satisfying certain criteria such as frame/subframe groupings where the different groups are associated with the different first and second UEs. Such frame/subframe groups can be configured together with the C-RNTI, at least at the time when the same C-RNTI is assigned to the later-coming UE.
As a prelude to detailing the exemplary embodiments of the invention,
As noted above the DL-CCH is used for allocating the DL-SCH resources for a certain UE. The UE identifier is transmitted in some form on the DL-CCH to indicate the specific UE to which the allocation on the DL-SCH is granted. This is the UE's temporary cell identifier noted above. For example, the UE identifier may be transmitted explicitly in the DL-CCH, it may be encoded, the scheduling grant in the DL-CCH may be encrypted or otherwise encoded with a key which is the UE identifier or which is a function of the UE identifier, or the DL-CCH itself which is directed to the particular UE can be channel coded using the UE identifier as one of several coding parameters. There are many other options available, but the point is that the UE identifier is used in some manner so that only the UE to whom the DL-CCH is directed can read the relevant contents. More generally, the UE identifier is transmitted explicitly or implicitly in a specific frame of the DL-CCH.
In many cellular systems the UE identifier is assigned to the UE upon the UE becoming established in the cell, upon the UE becoming connected in a non-idle state, after a random access procedure, after a handover from an adjacent cell, or by other means. In any event it is the network which assigns the UE its temporary identifier for use in the cell.
Transmission of data according to
When the UE detects its identifier and a channel allocation on the DL-CCH (point A in
The UE then transmits an ACK or NACK on the UL-CCH depending on the success of the data reception. In the example in
In the above chain of transmissions no new channel allocations via the DL-CCH are needed in some systems such as LTE, because the NACKs (points C and E) implicitly act as an agreement that the same channel is used for the retransmissions at fixed or preconfigured delays. The retransmissions are usually implemented with HARQ, but different radio systems may use different retransmission methods and still take advantage of the teachings herein.
There may be several chains of data retransmissions present in parallel.
The feedback for retransmissions (points C and E) is sent on the DL-CCH, i.e. the same channel as the channel allocations (point A). Retransmission at point D which results in the ACK/NACK feedback at point E assumes the feedback from the network at point C was a NACK. Typically the network will transmit the UE identifier along with the NACK (point C) as well as with the ACK (point E) responses to the UE's UL data (points B and D respectively).
Another transmission chain in
In certain practical network implementations,
In view of the interrelationships among logical channels for both UL and DL data transmissions as detailed for
The number of unique identifiers which any given cell has for use among its UEs is usually limited and designed so that adjacent cells are not using the same ones. As noted in the background section above the radio environment is changing so that this limited number of UE identifiers per cell may become a limiting factor. Exemplary embodiments of these teachings provide a method to use the same UE identifier for more than one UE in a cell and still avoid the signaling of
Firstly,
Various embodiments of the control channel transmissions ‘utilizing’ the identifier are given above, with both explicit and implicit utilizations detailed. Below are given various exemplary but non-limiting embodiments of how the eNodeB might enforce or otherwise purposefully bring about the predetermined time domain division so it can selectively associate different individual control channel transmissions (either or both of DL and UL control channel transmissions) with only one or the other of the first and second UEs.
At block 306 the predetermined time domain division comprises discontinuous reception DRX periods assigned to the first and to the second UEs in which those DRX periods have mutually exclusive reception time periods. In this manner while the first UE has a listening slot and checks the DL-CCH for its assigned (same) identifier the second UE is in a de-powered state to reduce its power consumption. Since the DRX periods are mutually exclusive in their reception time periods then when the second UE has an active listening slot the first UE is in a power saving mode and not listening on the DL-CCH.
The further examples at
One particular embodiment of block 308 is detailed at block 310; the mutually exclusive radio frame or subframe groups are even and odd numbered radio frame or subframe groups. In this example there are only two UEs sharing the same temporary cell identifier so there only needs to be two groups, even and odd frames in this case (or equivalently even and odd subframes without regard to frame number). The first UE configured with the same identifier and odd frames/subframes would then use the identifier, but would be allowed to receive and transmit the identifier only in odd frames/subframes. The second UE can then use the same identifier, but only in the even frames/subframes. Note that both UEs could in principle use any frames in the UL-SCH and DL-SCH since those logical channels are not used to carry the identifier information, but the time domain restriction applies on the even or odd frames on the UL-CCH and the DL-CCH.
The grouping of the frame numbers could in practice use more complicated methods so that the same identifier can potentially be used with more than only two UEs. In principle any mathematical formula could be used to derive grouping of the frames and/or subframes, as long as the formula produce an unambiguous group identifier from the frame and/or subframe numbers. Said another way, the different grouping have mutually exclusive sets of either frames and/or of subframes. Different rules must usually be applied on different channels. Referring to
As an example of this, the radio frames in LTE which are numbered with the SFN are divided into 10 subframes. The HARQ process cycle is 8 subframes. One way to conveniently to divide the subframes into 8 groups is with the formula:
Group—id=(10*SFN+subFN+offset) mod 8.
In this formula SFN is the system frame number, subFN is the subframe number ranging between 0 . . . 9, and offset is the channel-specific offset that is needed to handle the timing differences of different channels in the manner noted above for the LTE system (or in a different manner for other systems). If instead there is needed only 4 or 2 groups the modulo operation can be changed from mod 8 to mod 4 or mod 2, respectively. This formula is particularly useful when the data rates are rather high and the delay requirements are stringent.
Block 312 of
Group—id=(10*SFN+subFN+offset) mod X;
in which SFN, subFN and offset are defined above and X is selected from the group 2, 4, and 8. These values for X provide the best performance, but other values of X can also be used so more generally X can be any integer greater than one.
This next example shows a coarser frame grouping and defines the groups by the following formula:
Group—id=(SFN div GS) mod GN
In this formula SFN is again the system frame number, GS is the group size, and GN is the number of groups. Consider an example in which the frames of the system are 10 ms long, the GS value is set to 6 and the GN value is set to 10. The result would be a scheduling where each UE would have 60 ms active time in every 600 ms. The individual UE would be allowed to receive and transmit its ID during the active period only, which is mutually exclusive of the 60 ms active period of any of the other UEs (up to 9 others since GN=10) sharing this same UE identifier in the cell. This is shown at block 314 of
Where completion of the (HARQ) re-transmission chain as detailed in
Group—id=((SN*SFN+subFN+offset) div GS) mod GN
Meanings of these terms are all detailed above, and this formula is shown at block 316 of
This variant is more advantageous in cases where the UEs sharing the same identifier are not anticipated to need urgent data transmission and the amount of data is low. It is also necessary that there are other UEs in the cell that are not configured with any frame division, because this embodiment does not use the shared channels efficiently. But this is a moderate requirement, because it is very probable that in a practical deployment the UEs using this frame division technique will constitute a minority in terms of data volumes although they might form the majority of UEs in the cell (e.g., those UEs consuming the cell's identifier pool which in LTE is the C-RNTI pool).
Such blocks and the functions they represent are non-limiting examples, and may be practiced in various components such as integrated circuit chips and modules, and that the exemplary embodiments of this invention may be realized in an apparatus that is embodied as an integrated circuit. The integrated circuit, or circuits, may comprise circuitry (as well as possibly firmware) for embodying at least one or more of a data processor or data processors, a digital signal processor or processors, baseband circuitry and radio frequency circuitry that are configurable so as to operate in accordance with the exemplary embodiments of this invention.
Reference is now made to
The first UE 10 includes processing means such as at least one data processor (DP) 10A, storing means such as at least one computer-readable memory (MEM) 10B storing at least one computer program (PROG) 10C, and also communicating means such as a transmitter TX 10D and a receiver RX 10E for bidirectional wireless communications with the network access node 12 via one or more antennas 10F.
The network access node 12 similarly includes processing means such as at least one data processor (DP) 12A, storing means such as at least one computer-readable memory (MEM) 12B storing at least one computer program (PROG) 12C, and communicating means such as a transmitter TX 12D and a receiver RX 12E for bidirectional wireless communications with the UE 10 via one or more antennas 12F. There is a data and/or control path, termed at
Similarly, the S-GW/MME 14 includes processing means such as at least one data processor (DP) 14A, storing means such as at least one computer-readable memory (MEM) 14B storing at least one computer program (PROG) 14C, and communicating means such as a modem 14H for bidirectional communication with the network access node 12 via the control link. While not particularly illustrated for the UE 10 or network access node 12, those devices are also assumed to include as part of their wireless communicating means a modem which may be inbuilt on a radiofrequency RF front end chip within those devices 10, 12 and which chip also carries the TX 10D/12D and the RX 10E/12E.
For completeness also is shown the second UE 11 which includes its own processing means such as at least one data processor (DP) 11A, storing means such as at least one computer-readable memory (MEM) 11B storing at least one computer program (PROG) 11C, and communicating means such as a transmitter TX 11D and a receiver RX 11E for bidirectional wireless communications with the access node 12 via one or more antennas 11F.
At least one of the PROGs 12C in the access node 12 is assumed to include program instructions that, when executed by the associated DP 12A, enable the device to operate in accordance with the exemplary embodiments of this invention, as detailed above. In this regard the exemplary embodiments of this invention may be implemented at least in part by computer software stored on the MEM 12B which is executable by the DP 12A of the access node 12, or by hardware, or by a combination of tangibly stored software and hardware (and tangibly stored firmware). Electronic devices implementing these aspects of the invention need not be the entire devices as depicted at
Various embodiments of the computer readable MEMs 10B, 11B, 12B and 14B include any data storage technology type which is suitable to the local technical environment, including but not limited to semiconductor based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory, removable memory, disc memory, flash memory, DRAM, SRAM, EEPROM and the like. Various embodiments of the DPs 10A, 11A, 12A and 14A include but are not limited to general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and multi-core processors.
Further, some of the various features of the above non-limiting embodiments may be used to advantage without the corresponding use of other described features. The foregoing description should therefore be considered as merely illustrative of the principles, teachings and exemplary embodiments of this invention, and not in limitation thereof.
